Following its approval of the cellular radio concept in April 1981, the Federal Communications Commission was deluged with license applications for the operation of cellular radio systems in the ninety largest U.S. markets. The enthusiastic, widespread adoption of cellular radio technology may well effect the greatest change in communications since the invention of the telephone. The advantage of cellular radio for mobile telephone systems is "frequency reuse," in which a limited spectrum of radio frequencies can be made to serve many users much as TV stations from one area to another reuse channels in the VHF band. Instead of covering an entire service area with one transmitter with high power and an elevated antenna, cellular service relies on transmitters of moderate power distributed throughout a service area, each of which is only powerful enough to communicate with the radio telephones in its immediate area or "cell." A central microprocessor teamed with more specialized radio equipment keeps track of each mobile unit and assigns new frequencies to the units as they move across the cell boundaries. Users will be able to move from one cellular system to another system without loss of service by a "roaming" feature that identifies foreign equipment to the new system and informs the home system of the user's location. Calls coming into the home system for the user are rerouted to the correct foreign system.
The low power requirement of cellular radio transceivers gives cellular radio another significant advantage over conventional radiotelephone systems: The cellular radio telephone can be made small enough to be carried in one hand.
In early 1982, AT&T estimated that the immediate pent-up demand for cellular radio systems was 1.5 million units at monthly charge of about $150 per month. [Communications News, March 1982, p. 36]. The demand for cellular radio systems is expected to grow rapidly. VFI Communications extimates that there will be a demand for up to 3.5 million cellular radio units by the mid-1980s and for more than 30 million units by the year 2000, with revenues rising from a multi-billion dollar figure within a year after start-up to $10-60 billion by 2000. [Communications News, September 1982 p. 20]. Some telecommunications experts are even more optimistic, and believe that cellular radio will completely replace the wired telephone network by soon after the turn of the century. [Communications News, August 1982, p. 46].
Because cellular radio operates in a full-duplex mode, separate frequencies are required for transmit and receive. Furthermore, crowding in the lower frequency ranges has prompted the FCC to specify frequencies closely approaching the GHz range for cellular radio operation, with 825-845 MHz and 870-890 MHz being stipulated for transmission and reception, respectively. This 65 MHz range of operation requires the use of an antenna having a very low voltage standing wave ratio (VSWR) and a nearly flat gain response over a relatively wide frequency range, with an effective bandwidth of about four percent. However, antennas of conventional design operating in the VHF or low UHF range, other than those of the discone and rhombic types, typically have VSWRs above 1.5 and narrow bandwidths no greater than two percent. Because of the narrowband characteristics of conventional antennas, which are usually of the half-way type, they are typically tuned to the center frequency of the transmit range, resulting in a severe mismatch in the receive range. One workable, albeit awkward, solution requires the use of two separate antennas; one being tuned to the center frequency of the transmit range, the other to the center frequency of the receive range.